New tools help forecast tropical storms

A satellite image of Hurricane Bret, taken Aug. 22.

September 7, 1999
Web posted at: 4:07 p.m. EDT (2007 GMT)

An arsenal of satellite-based visualization tools developed at the University of Wisconsin at Madison is helping forecasters improve early-warning systems for tropical storms.

The tools are giving forecasters a detailed look at the anatomy of typhoons, cyclones and hurricanes, allowing them to break down the components of tropical storms and dissect some of the forces that create, steer and fuel these frequently dangerous weather phenomena.

The National Hurricane Center in Miami, Fla., and the Joint Typhoon Warning Center in Pearl Harbor, Hawaii, are currently using the satellite images.

"What we're doing is fusing together images through the use of multiple satellites," said Chris Velden, a tropical cyclone researcher and head of the university's Cooperative Institute for Meteorological Satellite Studies. "Each satellite has its own view of the Earth, and we're piecing many of them together for a more complete picture."

CIMSS is working to eventually combine satellite-based data with information from radar and aircraft to produce storm images in three dimensions, which could lead to more accurate forecasts and greater public safety. "We develop these tools in tandem with the forecasters," said Velden. "They know what they're looking for from us to aid the forecasting problem."

Wavetrak, one new tool introduced this year, combines data from five different satellites to create a 10-day movie of atmospheric waves circulating out of central Africa, the birthplace of cyclones. Created by Velden and research intern Jason Dunion, Wavetrak is designed to study the atmospheric waves that act as a conveyor belt carrying the right conditions that cause cyclones.

An example of the vertical wind shear field over the Atlantic including tropical cyclones Cindy, Dennis and Emily (red icons). Wind shear has a major impact on tropical cyclone intensity.

"We're grappling with how and where these waves originate, because about one in every ten will form into a named tropical storm," Velden says. "This shows us the amplitude and strength of these waves as they come off Africa and into the Atlantic."

Wavetrak allows scientists to get a complete picture of a cyclone, from its beginning over central Africa, its growth across the Atlantic to its eventual fizzling out. "It gives us an idea of exactly where they initiate over the African continent and their convective structure as they track over the ocean," said Velden. Another product developed by the CIMSS team measures the intensity of tropical cyclones — violent rotating windstorms. More specifically, the tool is giving forecasters a better handle on wind shear, which is essentially the difference in speed between high-level and low-lying winds. Wind shear is an important factor in predicting the intensity of a cyclone.

A strong wind shear can knock the tops off of cyclones and reduce their power. The CIMSS site provides a multi-colored map, which uses high-resolution satellite observations updated every three hours that show the levels of wind shear across the Atlantic. Scientists want to pinpoint the thresholds of wind shear effects, good or bad, on cyclones, said Velden.

Other CIMSS tools to track hurricane intensity include the Objective Dvorak Technique, the Advance Microwave Sounding Unit and super-rapid scanning.

The Dvorak technique, new this year, uses a computer-based algorithm (a step-by-step problem solving process) which provides atmospheric scientists with an automated satellite-based tool for estimating hurricane intensity. "This helps take the human guesswork out of it, and makes it totally computer-based," said Velden.

By using microwave transmissions, the Advance Microwave Sounding Unit has the ability to penetrate cloud cover and record the unique temperature signatures of hurricane cores. Core temperatures are closely related to intensity and AMSU provides color-coded images of those core hotspots.

Super-rapid scanning takes satellite images every 60 seconds and turns them into precisely detailed motion pictures of a storm. Hurricane forecasters must give a 24-hour advance notice in requesting these scans because so much data is being collected.

CIMSS is part of University of Wisconsin at Madison's Space Science and Engineering Center, which specializes in atmospheric studies of earth and other planets. It is supported by NASA and the National Oceanic and Atmospheric Administration.

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